I am working something pretty similar...
For controlling editing, I solved by using conditional formatting, applying a read only format to a control if userName() not equal to requestor (or in your case "Initiator").
For email, I used concat() function in the To: section of the email submit...looks something like concat(user1," ; " user2," ; ",user3). However, I believe there is a limit on that. I am working with relatively small numbers.
I am also not on SP, just an Access DB and SQL. A little low tech, but it's getting the job done :)